The present invention is directed to scanning beam devices. More specifically, the present invention is related to methods and systems for counterbalancing a drive assembly in a scanning fiber device.
There is a growing market for micro-optical displays and small image acquisition systems (e.g., cameras). Scanning beam systems fill the need, but the lack of low cost micro-optical systems with a wide field of view (FOV) have been the most significant barrier for reducing the size of scanning beam systems for use in minimally invasive medical imaging (flexible endoscopes), surveillance, industrial inspection and repair, machine and robotic vision systems, and micro-barcode scanners.
To that end, an improved scanning beam system has recently been developed by the University of Washington which involves the use of a cantilevered optical fiber that is scanned in one or two dimensions to project light out of the end of the optical fiber to form an image on a target area. In addition to image formation and micro-display applications, image acquisition is also possible with the addition of a sensor, such as a photosensor. To acquire an image, the light projected out the end of the cantilevered, scanning optical fiber is reflected from the target area and the backscattered light is captured and measured with the sensor in time series. Because the motion of the optical fiber is predictable and repeatable, the reflected light intensity measured at the sensor can be sequentially correlated with the known position of the optical fiber, and a two-dimensional image may be created one ‘pixel’ at a time. Some exemplary scanning fiber devices of such type are described in U.S. Pat. No. 6,294,775 B1 (Seibel) and U.S. Pat. No. 6,563,105 B2 (Seibel) and U.S. Patent Application Publication Nos. 2001/0055462 A1 (Seibel) and 2002/0064341 A1 (Seibel), the complete disclosures of which are incorporated herein by reference.
In comparison to traditional scanning beam devices, scanning fiber technology offers many advantages. The small mass of the optical fiber scanner allows high scan angles at video rates—typically between about 1 kHz and about 50 kHz, and preferably between about 5 kHz and about 25 kHz. Optical fiber scanners also have a smaller ‘footprint’, taking up less space and can be conveniently packaged into a small (<1 mm) diameter cylindrical endoscope or catheter housing.
While the scanning fiber systems have proven to be useful, improvements are still needed. For example, current scanning fiber systems that scan the optical fiber about two-axes typically include an actuation element or drive assembly coupled to the scanning element. The scanning element (e.g., optical fiber) extends from a distal end of the drive assembly so that actuation of the drive assembly causes the optical fiber to move in a periodic motion that substantially corresponds to the motion of the drive assembly. As can be appreciated, actuation of the drive assembly will often cause transverse forces (e.g., accelerations) and torques to the scanning fiber device which may detrimentally affect image formation and image acquisition of the target area. There is also a relatively very small axial force on the fiber. This small axial force is caused by the distal tip of the drive assembly and the scanning fiber moving in an arc in one axis, or part of a spherical surface in two axes. This small axial force, and subsequent small movement, does not typically affect the scan quality.
In order to stabilize the drive assembly and to decrease the free end amplitude of motion of the drive assembly, it was found that a stationary object may be attached to a proximal end of the drive assembly. Preferably, the stationary object is typically many times more massive (e.g., typically between about twenty times as massive and forty times as massive) than the drive assembly and the optical fiber. While such a solution may be useful for larger scanning fiber devices, because the dimensions of small scanning fiber devices (e.g., flexible endoscope) are so small, it may not be possible to place a mass of an appropriate size within the housing of the scanning fiber device to minimize the drive assembly's proximal end attachment movements.
Consequently, what are needed are methods and devices that can counterbalance the forces and/or torque created by the movement of the drive assembly and scanning element.